1. Field of the Invention
The present invention relates to a high power, high capacity, rechargeable battery that has an improved connecting structure between unit cells. The present invention also relates to a battery module using the rechargeable battery.
2. Discussion of the Background
There exists a need to develop a high power rechargeable battery that uses a non-aqueous electrolyte and has high energy density. Such a battery may be used in low capacity batteries in which battery cells are packaged into packs that serve as power sources for various portable small electronic devices such as cellular phones, laptop computers, and camcorders. Alternately, a high capacity rechargeable battery in which several tens of battery cells are connected in series or in parallel may be used as a power source for driving motors such as in a hybrid automobile.
Such a high capacity rechargeable battery or battery module is typically assembled by connecting a plurality of rechargeable batteries together in series to form a unit cell. Each unit cell is comprises an electrode assembly, a case, and a cap assembly.
That is, the unit cell may be fabricated into various shapes such as cylindrical and rectangular. An electrode assembly of the unit cell may comprise a bar of positive and negative electrode sheets and an insulator separator interposed therebetween that are wound together as in a jelly roll and are inserted into a case. The case is mounted with a cap assembly formed with outer terminals to provide a battery.
A rectangular unit cell having the above-mentioned structure is disclosed in Japanese Utility Application Laid-Open No. H06-86259. It also discloses a structure that has a cap with terminals protruding from the surface of the rectangular case.
However, since the rechargeable battery disclosed in the publication has terminals on only one side surface of the battery, it is difficult to connect unit cells together and the utilization of the battery is limited. That is, the positive electrodes and the negative electrodes of the electrode assembly are mounted with a conductive tab or a current collecting plate that collects current that is generated when operating the battery. The tab or the current collecting plate is connected with a positive electrode terminal and a negative electrode terminal that is mounted on the cap assembly via a lead to introduce the current that is generated in the positive electrode and the negative electrode to the positive electrode terminal and the negative electrode terminal, respectively.
However, since the above-mentioned positive electrode terminals and negative electrode terminals are mounted on only one side of the cap assembly, a separate connecting member is required to join the unit cells to provide a battery module. Therefore, it is difficult to connect the unit cells and the space utilization is deteriorated.
FIG. 5 shows a battery module 100 according to the prior art in which units cells are connected in series. According to FIG. 5, the positive electrode terminal 114 and the negative electrode terminal 115 that protrude on the upper surface of the cap assembly 113 of each unit cell 111 are positioned beside the negative electrode terminal 115 and the positive electrode terminal 114 of the adjacent unit cell 111, respectively. The connection members 116 connect the threaded negative electrode terminals 115 and positive electrode terminals 114 via nuts 117, 118.
If the lower part of the case of the unit cell according to the prior art is positioned to face the floor, since both the positive electrode terminal and the negative electrode terminal are disposed on only the upper part of the case, the unit cells may have to be arranged beside each other to connect with each other in series or in parallel. Thus, the unit cells are positioned inefficiently with respect to a certain unit space.
This problem becomes more serious for hybrid electric vehicles that require numerous unit cells confined to a certain space to provide high capacity and high power. As the aforementioned unit cells of the prior art must be arranged in only one configuration the capacity and power are deteriorated per unit area are reduced.
In addition, in order to provide a battery module according to the prior art, several or several tens of unit cells are connected using nuts. The insulation of the nuts is difficult and time consuming, so the cost thereof is increased.